Fat-level measurements used to indicate individual body condition and fitness are useful only when taken at a region along the body where fat responds to variations in caloric intake. Investigations to identify appropriate species-specific regions are limited, especially for cetaceans that have a specialized fat (blubber) that serves as an energy reserve and provides insulation. Over 18 mo, body mass of six pilot whales varied (range: 50–172 kg), and although caloric intake increased when water temperatures were lower, generally the best-fitting state-space model for length-adjusted mass was based on a single factor, caloric intake. After correcting for body length (range: 330–447 cm), the slope for blubber thickness and “blubber ring” thickness (average blubber thickness along a girth) in relation to body mass was positive and had a P value of <0.10 at six of 16 blubber measurement sites and one of five girth measurement sites, respectively. The slope for body girth (a reflection of changes in underlying blubber thickness) in relation to body mass was positive and had a lower P value (P<0.10) at three of five girth measurement sites. Results indicate that blubber from the anterior insertion of the pectoral fins to the posterior insertion of the dorsal fin is the most metabolically active region. This region includes the midflank site, a location where blubber thickness measurements have historically been taken to monitor cetacean body condition. Conversely, blubber in the peduncle region was comparatively inert. These findings must be considered when measuring blubber thickness and body width (i.e., photogrammetry) to monitor the condition of free-ranging cetaceans.
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